The present invention relates to a power window of a vehicle such as an automobile which is opened and closed by a drive source such as an electric motor, and more particularly to a safety device for and a method for operating such a power window which, when a person's hand, head, etc., is caught between the window glass and the sash, detects such fact to perform a safety control operation.
In general, a power window of a vehicle is operated (opened and closed) by an electric motor or the like. Sometimes the hand or head of the driver or passenger or some other object (collectively hereinafter referred to as "a foreign object" when applicable) may be caught between the window glass and the sash. In order to prevent such an accident, there has been provided a safety device, which detects a foreign object caught in the window and immediately stops the movement of the window glass or moves the window glass so as to open the window, thereby to prevent the occurrence of an accident.
To this end, the safety device employs a detecting device for detecting the drive current of the electric motor which drives the window glass. When a foreign object is caught between the window glass and the sash, the load on the motor increases, and therefore the current of the motor also increases. The increased current is detected by the aforementioned detecting device. Upon detection of the foreign object, the window glass is forcibly moved to open the window, thereby to release the foreign object.
However, in the above-described safety device where an increase in motor current is utilized for detecting the fact that a foreign object is caught by the window glass, in practice there is a finite time lag between the occurrence of a dangerous state and the detection of the increase in motor current. Therefore, the detecting method suffers from a problem that the safety control operation is slow in response; that is, when the dangerous situation occurs, the safety control operation can only be carried out after a certain time delay. Hence, for instance, if someone's neck is caught between the window glass and the sash, the person is apt to suffer pain for several seconds. Thus, the conventional detecting method is not entirely satisfactory.
Also, the present applicants have previously proposed a safety device in which the rate of change of the speed of rotation of the motor is detected, that is, the relative speed of the motor is detected. When the relative speed falls below a predetermined value, it is determined that a foreign object has been caught in the window, whereupon the motor is stopped or rotated in the opposite direction to forcibly move the window glass in the window opening direction.
In an ordinary power window system, the torque of the motor is transmitted through a gear mechanism or the like to the window glass, and therefore backlash may occur at the start of the motor. In this case, at the start of the motor the speed of rotation of the motor is momentarily increased and then abruptly decreased. Hence, the above safety device which detects a decrease in relative motor speed to perform the safety control operation sometimes can erroneously detect that a foreign object has been caught in the window, and in response to this erroneous detection erroneously effect a safety control operation.